The disclosure relates to a slip-controlled hydraulic vehicle brake system having the features described below.
German Offenlegungsschrift DE 195 01 760 A1 discloses a slip-controlled hydraulic vehicle brake system, the brake circuits of which are connected via isolation valves to a brake master cylinder. It has wheel brakes, which are connected via pressure buildup valves to the isolation valves and via pressure lowering valves to a suction side of a hydraulic pump. For wheel-specific brake pressure control, each wheel brake has a pressure buildup valve and a pressure lowering valve. A hydraulic pump is provided in each brake circuit, wherein the hydraulic pumps of the brake circuits are driven jointly by an electric motor as a drive or pump motor. Hydraulic pumps in slip-controlled vehicle brake systems are also referred to as return pumps. For a rapid brake pressure buildup when the brake master cylinder is not actuated and the vehicle brake system is unpressurized, the known vehicle brake system has an intake valve, by means of which a suction side of the hydraulic pump can be connected to the brake master cylinder. The pressure buildup valves and pressure lowering valves can be regarded as wheel brake pressure modulation valve arrangements, by means of which wheel brake pressures can be controlled in each vehicle wheel on a wheel-specific basis. In this way, antilock control, traction control and vehicle dynamics/antiskid control operations are possible, for which abbreviations such as ABS, ASR, ESP and FDR are customary. These slip control operations are known per se and will not be explained in greater detail here.
In German Offenlegungsschrift DE 10 2010 043 403 A1, the hydraulic pump in one brake circuit is replaced by three hydraulic pumps or hydraulic pump elements connected hydraulically in parallel, which are driven jointly.
For the hydraulic pumps of such vehicle brake systems, there are two requirements, which are diametrically opposed: on the one hand, they must be capable of pumping brake fluid against a brake pressure prevailing in the vehicle brake system when the brake master cylinder is actuated. In this case, the prevailing pressure is very high when the brake master cylinder is actuated with maximum muscle power by a vehicle driver. The hydraulic pump and the drive motor must not come to a halt. The opposite case is a brake pressure buildup when the brake master cylinder is not actuated and the vehicle brake system is unpressurized, which requires a large delivery volume flow from the hydraulic pump to achieve a rapid pressure buildup. Achieving a high or even the maximum pressure is not decisive here, a moderate or medium pressure being sufficient. The rapidity of the pressure buildup and, associated with this, the rapidity of actuation of one or more wheel brakes is crucial in a vehicle dynamics/antiskid control operation because a tendency for a vehicle to skid can only be counteracted effectively by a very rapid braking intervention at one or more vehicle wheels: the more rapid the braking intervention, the more effectively a tendency to skid can be counteracted. The two requirements lead to a hydraulic pump which is per se overdimensioned and to a drive motor which is per se overdimensioned. A relatively large and heavy drive motor with a high electric power consumption, which does not come to a halt, even at the maximum brake pressure in the vehicle brake system, but drives the hydraulic pump, is required.